Bulky Phosphazenium Salt Controlling Chemoselective Terpolymerization of Epoxide, Anhydride and CO 2 : From Well‐Defined Block to Truly Random Copolymers

Copolymers with precise compositions and controlled sequences are great appealing for high‐performance polymeric materials, but their synthesis is very challenging. In this study, tetrakis[tris(dimethylamino)phosphoranylidenamino] phosphonium chloride (P5Cl) and triethylboron (TEB) were chosen as the binary catalyst to synthesize both well‐defined block and truly random poly(ester–carbonate) copolymers via the one‐pot/one‐step terpolymerization of epoxide/anhydride/CO 2 under metal‐free conditions. The bulky nature of phosphazenium cation not only led to loose cation–anion pairs and enhanced the reactivity, but also provided the chain‐end an appropriate protection and improved the controllability. In particular, P5Cl/TEB with a molar ratio of 1/0.5 showed an extraordinary chemoselectivity for ring‐opening alternating copolymerization (ROAC) of cyclohexene oxide (CHO) and phthalic anhydride (PA) first and then ROAC of CHO/CO 2 . Thus, well‐defined block polyester–polycarbonate copolymers were synthesized by CHO/PA/CO 2 terpolymerization. The chemoselectivity was easily tuned and the ROAC of CHO/PA and ROAC of CHO/CO 2 occurred simultaneously with P5Cl/TEB=1/2, producing truly random poly(ester–carbonate) copolymers from CHO/PA/CO 2 . In addition, this P5Cl/TEB catalyst and the strategy to regulate its chemoselectivity are versatile for various anhydrides, epoxides and initiators. Thus, poly(ester–carbonate) copolymers with varying sequences, compositions, and topologies are successfully synthesized, making it possible to compare their properties and to expand their applications.